Ionization chamber for mass spectrometer



Nov. 3, 1959 J. A. RIcKARD ETAI- 2,911,531

IONIZATION CHAMBER FOR MASS SPECTROMETER Filed March 12, 1956 2 Sheets-Sheet l INVENTORS F/G. v James A. fP/c/mra',

BY Alex F rose/7,

1959 J. A. RICKARD ET L IONIZATION CHAMBER FOR MASS SPECTROMETER Filed March 12. 1956 2 Sheets-Sheet 2 INVENTORS. James A. Rickard, BY Alex FI'OSC/I,

2,911,531 Eatented Nov. 3, 1959 p 2,911,531 a v it IONIZATION CHAMBER or: MASS; V l SPECTROMETER. f 1.. James A. Rickard, Bellaire, and'Alex' Frosch, Houston,

Tex., assignors, by mesne assignments, to Jersey Production Research Company, Tulsa,- Okla.,-a corporation ofDelaware Application March 12,1956, Serial No. 571,026

l isClaims. c1. zen-41.9

This invention relates to the art of mass spectroscopy. More particularly this invention relates to a new and improved source of ions for use in mass spectroscopy.

An ion source assembly includes therein a tube connected to a vacuum pump which is utilized to maintain a vacuum within the tube. Located within the tube is an ionization chamber utilized :to ionize a sample, the sample being usuallya gaseous .material but may be of solid material. A means for emitting electrons such as a filament is usually located adjacent to a slit in the ionization chamber. The ionization chamber having a higher potential than the filament attracts the electrons. The electrons move through the ionization chamber resulting in the ionization of the sample molecules within the chamber. A plurality of accelerating plates, each having a slit centrally disposed therein and each being at an appropriate positive potential, are mounted below the ionization chamber for accelerating the ionized molecules toward the analyzingregion of the mass spectrometer.

In currently utilized mass spectrometersa magnetic element or electromagnetic element is positioned outside of the tube. The magnetic element is positioned so as to guide the beam of'electrons from the electron emitting means directly over the slits of the accelerating plates. The magnetic element is generally movable with respect to the vacuum tube. If the ionization chamber is also movable several disadvantages may result, a few of which are: 1

(1) the position of the magnetic element is critical and must be so positioned as to direct the path of the electrons directly over the long axes of the accelerating plates. Since the magnetic elements are outside of the vacuum tube and the ionization chamber is inside of the vacuum tube and they are both separately adjustable, adjustment of the magnetic element after the ionization chamber has been adjusted to its proper position is difiicult and time consuming.

(2) because of the separation of the magnetic element from the ionization chamber the fringe effects of the magnetic field often cause the ionized molecules which are being accelerated through the acceleration plates to be deflected and hence not passed through the slits in the acceleration plates.

It is an object, therefore, of our invention to provide a new and improved ion source having magnetic means attached thereto so as to be movable with the ion source and which is small and compact thereby decreasing the fringe effect of the magnetic field. I

Briefly described our new ion source assembly includes a housing enclosing a; space of reduced pressure. An ionization chamber is mounted within the housing. Also mounted within the housing rather than outside of the housing is a magnetic member having its magnetic poles positioned so as to cause the electrons emitted from the filament to move along a path directly over the longitudinal axes of the slits within the accelerating =2 I platesQ The magnetic member is integrally connected to the ionization chamber so as to move with the ionization cham ber thereby providing for the automatic proper, positioning of the magnetic member when the ionizing chamber is moved within the housing. Since the magnetic member is mounted within the housing rather than outside of the housing the fringe effects of the magnetic field are held to a minimum.

Other objects and a fuller understanding of the invention may be had by referring to the following description-and claims, taken in conjunction with the accompanying drawings in which: i

Fig. l is a drawing illustrating a preferred embodiment;

Fig. 2 is an elongated isometric view showing in more detail the ionization chamber and accelerators of the preferred embodiment;

Fig. 3 is a plan View of the ionization chamber; and

Fig. 4 is a sectional view taken along line 44 of Fig. l.

Referring to the drawings and more particularly to Fig. 1,,numeral 10 is a housing which may be a vacuum pump housing. Located within the housing and cantrally thereof is a tubular member 11 which has its free end 12 projecting into 'the housing 10. The free end 12 of the tubular member 11 is provided with a slot 13 into which are arranged pins or projections 14 which are rigidly connected to a second tubular member 15.

Threadedly connected to the first tubular member 11 by mating threads 16 is a ring gear17 which is provided with recesses 18 to receive the pins 14. The pins 14- are'held into the recess 18 by an annular member 19 which in turn is held in the ring gear 17 by screws 20.

The gear 17 is engaged meshingly with a pinion 21. The free end 22 of pinion 21protrudes by way of seal 23 through the vacuum-pump housing 10.

Second tubular'member 15 'has an' annular shoulder 24 upon which is positioned a plurality of glass posts 25. A plurality of accelerating plates 27, 28, 29 and 30 are mounted on glass posts 25 and spaced apart one from the other byv means of tubular glass spacers 26, 26a, 2619, 260, and 26d positioned concentrically on glass posts 25, as shown more clearly in Fig. 2. In Fig. 2 each of the accelerating plates 27 through 30 has centrally disposed therein a slit designated by numerals 70 through' 73, respectively, with the slit of one accelerating plate in register with the slits of the other accelerating plates. The tubular member 15 also has a slit 33 which is in register with the'slits of the accelerating plates.

Mounted upon'the posts 25 and 26 is a cylindrical member 40, the top of the cylindrical member 40 having bored-therein a first bore 41 and a second bore 42. The top of cylindrical member 40 also has bored therein a sample inlet 43 through which the sample to be analyzed, if it is a gaseous sample, may be introduced into the ionization chamber defined by a cylindrical wall 44 and top and bottom plates 65 and 66. The center of the sample inlet 43 is on the axis of the cylindrical member 40 and bisectsthe distance betw'een'the bores 41 and 42.

A pair of defining holes 45- and 46 are provided in the cylindrical wall 44. Defining holes 45 and 46 are horizontally spaced one from the other and lie in the same horizontal plane. Cylindrical member 40 has a substantially annular cut-out portion into which a magnetic member 60 is machine pressed, as best seen in Fig. 4. Recesses and 101 are provided adjacent defining holes 45 and 46, respectively. Located adjacent defining hole 45 is a means 47 having lead-in wires 48 for emitting an electron beam. The means for emitting an electron-beam may consist of a filament or any other well known elegemitting means 47 are attracted through defining hole 45 along a path such that they move across the chamber defined by the inner-cylindrical wall 44, through. the defining hole 46, and into the trap or anode 51. Hence, the sample molecules introduced into the space defined by the inner-cylindrical Wall 44 are subjected to a beam of electrons and ionized. Electrical potential is applied to housing 40 by means of electrode 102 (see Fig. 3). The filament 47, trap 51 and defining holes 45 and 46 are located in substantially the same vertical plane as the long axes of the slits within plates 27 through 30,

inclusive and the long axis of slit 33 in tubular member and slit 67 in bottom plate 66. The configuration of magnetic member 60 is best illustrated in Fig. 4. If desired, magnetic member 60 may be machine-press fitted into cylindrical member 40. The machine-press fit causes fewer air spaces to be present in themagnetic circuit and hence provides for a more efiicient magnetic circuit since the air spaces cause the reluctance of the circuit to be greatly increased. It can be seen that the magnetic cylindricalmember 60 is substantially annular in cross section. The magnetic member 60 has on its inner periphery a pair of diametrically spaced protrusions 61 and 62. Protrusions 61 and 62 are substantially in the same vertical plane as the filament 47 and trap 51 and hence are substantially in the same vertical plane as the slits 27 through 30 in the accelerating plates and the slit 33 in tubular member 15 and slit 67 in bottom plate 66. The major portion of the magnetic member 60 can be made of a soft iron material such as mu-metal including the protruding portions 61 and 62. However, in order to provide for permanent magnetization of magnetic member 60, portions of the magnetic member 60 are made of a permanent magnetic material such .as is shown at 63 and 64. Permanent magnetic portions 63 and 64 are diametrically opposite from one another and spaced 90 in azimuth from each of the protrusions 61 and 62. The magnetic polarity of the permanent magnetic portions 63 and 64 is such'as to cause the protrusions 61 and 62 to be of opposite magnetic polarity. Hence a magnetic flux exists across the space between the protrusions 61 and 62, which flux parallels a center line through holes 45 and 46. By the arangement, as described, the electron beam from filament 47 is directed by the magnetic member 60 through the defining holes and directly over the slits in the accelerating plates and tubular member 15 and slit 67 in bottom plate 66.

In operation a sample is introduced into the chamber defined by the cylindrical wall 44, top plate 65, and bottom plate 66 and is ionized by an electron beam from filament 47 which is directed across the chamber and into the trap 51. The ionization of the sample is caused by the bombardment of the sample by the electrons in the electron beam. The sample molecules thus ionized pass through the slits in the accelerating plates and into tubular member 11. The magnetic member 60 with its protrusions 61 and 62 which are of opposite magnetic polarity direct the electronic beam along a particular predetermined path directly over the slits in the acceleration plates and the tubular member 15 and slit 67 in bottom plate 66. Any adjustment of the ionization chamber is accomplished by moving the member 22 which causes rotation of the ring gear 17 and, therefore, moves the tubular member 15 along the longitudinal axis of the tubular member 11. The pins 14 in slots 13 resist the rotation of the tubular member 15 and allow the tubular member 15 to be moved from the position shown in Fig. 1 to a second position. Since the magnetic member 60 is integrally connected with the ionizing chamber the magnetic member 60 will be moved as a unit with the ionizing chamber defined by cylindrical wall 44.

It is clear, therefore, from the foregoing description of our new and improved ion source for use in mass spectroscopy that we have invented an ion source which permits theuser to automatically adjust the position of the magnetic-directing means with any change in position of the ionization chamber; Also because of the proximity ofthe magnetic member to the ionization chamberthe fringe effect of the magnetic field is held to a minimum.

Although we have described our invention with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example andth'a't numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What we wish to claim asnew and useful and to secure by Letters Patent is:

1. In an apparatus for use in mass spectroscopy: a housing enclosing a space of reduced pressure; a cylin- 'dricaLmember having an ionization chamber with a sample inlet movably mounted within said housing, said ionization chamber having a pair of spaced defining holes lying in the same horizontal plane;v means located adjacent one of'said holes at a different potential from said ionization chamber for emitting electrons through said hole and into the space defined by said ionization chamber for ionizing a sample within said ionization chamber; means adjacent said other hole for receiving said electrons; and a substantially cylindrical magnetic member mounted within said cylindrical member so as to be movable therewith, said magnetic member having permanent magnetic portions and a pair of protrusions of soft-iron on its inner periphery diametrically spaced, said protrusions being of opposite polarity and positioned so as to direct said flow of electrons along'a particular desired path.

2. In an apparatus for use in mass spectroscopy: a housing enclosing a space of reduced pressure; a cylindrical member having a sample chamber therein and a sample inlet mounted Within said housing, said chamber having a pair of spaced defining holes lying in the same horizontal plane; means located adjacent one of said holes at a different potential from said-chamber for emitting electrons through said hole and into said chamber for ionizing a sample within said chamber; means adjacent said other hole for receiving said electrons; a plurality of vertically separated accelerating plates mounted below said cylindrical member and movable therewith, each of said plates having a centrally located slit in register with the'slits of the other plates, the long axes of said slits being in substantially the same vertical plane as said electron emitting means; a substantially cylindrical magnetic member having permanent magnetic portions integrally mounted within said cylindrical member so as to be movable therewith, said magnetic member having a pair of protrusions of soft iron on its inner periphery diametrically spaced and in substantially the same vertical plane as said electron emitting means, the magnetic polarities of said protrusions being such as to cause the movement of the electrons .along a path through said defining holes and directly over the slits in said accelerating plates; and means for efifecting the movement of said cylindrical member and magnetic member longitudinally with respect to said housing.

3. In an apparatus for use in mass spectroscopy: a vacuum pump housing; a cylindrical member having a closed top and a bottom having a slot therein disposed within said vacuum pump housing, said cylindrical member having bored in the top thereof a trap bore and a filament bore, said cylindrical member also having a sample inlet in the top thereof the center of which is on the axis of said cylindrical member, the sample inlet bisecting the distance between said trap bore and said filament bore; an inner cylindrical wall within said cylindrical member and coaxial therewith and having a diameter less than the spacing between the filament bore and the trap bore, said inner cylindrical wall having two electron beam defining holes diametrically opposite one another and in the same horizontal plane; a filament eX- tending through said filament bore to a point adjacent one defining hole and trap member positioned adjacent the other defining hole whereby the molecules of a sample introduced into the space defined by said inner cylindrical wall may be subjected to a beam of electrons; a plurality of vertically separated accelerating plates mounted below said cylindrical member and movable therewith, each of said plates having a centrally located slit therein in register with the slits of the other plates, the long axes of said slits being in substantially the same vertical plane as said filament and said trap; a substantially cylindrical magnetic member mounted within an an nulus between the vertical cylindrical member and said inner cylindrical wall and having a diameter greater than the space between said filament and said trap, said magnetic member having protrusions diametrically disposed on its inner periphery, said protrusions being substantially in the same vertical plane as said filament and said trap,

said protrusions being of soft iron material, said magnetic member also having two portions thereof made of permanent magnetic material, said permanent magnetic portions being diametrically opposite and spaced in azimuth from each of said protrusions, the magnetic polarities of said permanent magnetic portions being such as to cause said protrusions to be of opposite magnetic polarity, whereby the magnetic flux between said protrusions effects the movement of the electrons in said electron beam along a path through said defining holes and directly over the slits in said accelerating plates; and means for effecting the movement of said cylindrical member longitudinally with respect to said vacuum pump housing.

Schaeffer: An Improved Mass Spectrometer Ion Source; in Review of Scientific Instruments, vol. 25, No. 7, July 1954, pp. 660662. 

